DESCRIPTION (From the Applicant's Abstract): This application concerns a new possibility for the role of Abeta in AD. It is designated to investigate the loss of synaptic plasticity and death of nerve cells caused by nonfibrillar Abeta oligomers. Oligomers accumulate in AD brain, and current best evidence indicates they contribute to disease progression, potentially accounting for the imperfect correlation with amyloid. Aims focus on three key properties of oligomers (referred to as "ADDLs," for Abeta derived diffusable ligands). (i) ADDLs inhibits LTP in under an hour, one of the fastest known responses to any form of Abeta. (ii) ADDLs kill hippocampal neurons by a mechanism blocked by germline knockout of Fyn, a protein tyrosine kinase coupled to NMDA receptors and tetanus-induced LTP. (iii) ADDLs bind to cell surface proteins that are trypsin-sensitive and cluster at punctate "hot spots." The goal is to understand the molecular basis for ADDL neurotoxicity. Two hypotheses will be evaluated. First, ADDLs may be small protein ligands that cause damage by disturbing Fyn signal transduction, a consequence mediated by specific toxin receptors. Alternatively, ADDLs may disrupt cell integrity with little or no specificity, generating a global breakdown of cell physiology that includes loss of LTP and culminates in cell death. Predictions of these hypotheses will be tested by the proposal's AIMs. Aim 1. LTP or neurotransmission-Is the synaptic impact of ADDLs specific for LTP, or is synaptic function broadly impaired. Aim 2. Types of plasticity-Do ADDLs affect multiple types of neuronal plasticity, or only tetanus induced LTP? Aim 3. Molecular impact-Does toxicity stem form ADDLs impact on Fyn, or do ADDLs attack at alternative and perhaps multiple sites? Aim 4. Cell surface reactions-Are ADDLs bound by specific "toxin receptors," or is ADDL activity not dependent on unique binding sites? Results from this application will give a new basis for understanding the actions of Abeta oligomers found in human brain. In a best-case outcome, findings would provide novel targets for therapies that ultimately could reverse and not just slow down AD memory impairment.